1. Field of Invention
This invention relates to an inkjet system (jettable solutions and receiver sheets) suitable for use in an inkjet recording process. It relates in particular to inkjet systems where recorded images can be observed by both reflected and transmitted light. Inkjet prints used at this present time have a need for improvement in physical and handling properties, particularly in water fastness, bleeding, humidity stability, light stability, reduced printhead clogging, as well as for improved image quality. In addition to the above deficiencies, the present dye systems used in inkjet have a restricted color space reproduction (i.e., are not able to produce the color gamut the human eye sees).
A preferred embodiment of this invention is therefore directed at an inkjet recording system with improved handling and performance characteristics. In particular, this system will give a recorded image that will overcome the shortcomings of the present systems by giving images that are resistant to rubbing smears, and bleeding remain intact upon contact with water, have good stability to humidity and light fading and will not cause clogging of the printhead; however, of utmost importance, the dye images produced will have improved color gamut and a photoreal appearance. All these benefits are obtained by the formation of an insoluble chromophore insitu (i.e., within the receiver matrix of this system). Furthermore, these are the same chromophore molecules used in present silver halide color photography, so color rendition is expected to be of photorealistic quality.
Inkjet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream inkjet systems, ink is emitted in a continuous stream under pressure through an orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the breakup point, the droplets are charged in accordance with digital data signals and passed through an electric static field, which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
This invention is intended for use in both types of systems. The continuous stream system may allow for more options in the practice of this invention by allowing for the in-line premixing of two reactants such as color former and alkali before droplet formation. However in this configuration recycling of unused components would not be feasible.
2. Background Art
The following list describes some of the major requirements of an inkjet recording system in order to achieve commercial success:
1. Sufficient ink absorbing capacity and ink receptivity of the receiver layer to prevent the ink/pigment from streaking and running during printing, even under conditions where several droplets are deposited in a rapid sequence onto the same spot.
2. Fast drying of the layer surface after printing of the image leading to prints free from tackiness.
3. Excellent color rendition, no change of print hue with time.
4. The ability to have a high-gloss surface. Chromophores must not have a dull, flat look.
5. Transparencies must be clear, transparent, light scatter-free.
6. Resistance of the surface of the image to rubbing smear.
7. Excellent water fastness and minimal bleeding of the produced images.
8. Excellent light fastness of the printed image.
9. Excellent archival stability (especially photoreal).
10. Chromophores that have proper spectral quality for producing excellent color rendition
11. Chromophores that have proper spectral quality so go as to have color gamut space capabilities similar to what the human eye can see.
12. Inks that do not cause clogging of printheads.
At the present time no available system successfully addresses all these requirements. A number of approaches have been attempted to achieve the requirements of a good inkjet print. Water fastness has been addressed by a variety of techniques. Thus solutions to the problem have been proposed for by specific formulations of the inks or alternatively by specific modifications of the receiving layer.
One approach to improve water fastness has been the use of reactive dyes (U.S. Pat. No. 4,443,223 Kissling et al) and U.S. Pat. No. 5,230,733 (Pawlowski et al) and references cited therein. Although some improvement has been achieved by this approach, in general, under the conditions of practical printing, the environment is less than optimal and therefore do not achieve full reaction of these dyes with a given binder.
Another approach to both water fastness and light fastness has been inks based on colloidal dye dispersions and polymers in inks. U.S. Pat. No. 5,100,471 (Winnik et al), U.S. Pat. No. 5,017,644 (Fuller et al), U.S. Pat. No. 5,224,987 (Matrick et al) U.S. Pat. No. 4,246,154 (Yao et al). Inks based on colloidal dyes as well as hot melt inks although yielding images of good light and water fastness do in most cases lack brilliance, color gamut and are not totally transparent.
The use of cationic polymers in the receiver layer in conjunction with acidic inks to induce water fastness as described in U.S. Pat. No. 4,783,376 (Sakaki et al) and U.S. Pat. No. 4,575,465 (Viola) do in general give good water fastness. Although water fastness can be gained with this method, severe drawbacks in light stability, archival stability, and hue shifts accompany this simple benefit.
The introduction of inorganic pigments, filters, minerals, metal salts, and metal oxide have been proposed. U.S. Pat. No. 4,116,910 (Rudolphy et al) claims improved light stability.
The addition of pigments and polymers to improve water fastness and drying is described in U.S. Pat. No. 5,104,730 (Misuda et al) and U.S. Pat. No. 4,879,166 (Misuda et al). They describe the use of porous recording sheets where the porous layer is mainly pseudo boehmite. Although a number of advantages are claimed using these methods, most layers obtained by these methods become very brittle with age, are slightly opaque and have steep color rendition thus poor color space. Improvements incorporated into the receiving layer and jettable solution, to meet the prestated requirements of modern inkjet printing technology, are therefore the objectives of this invention.
Accordingly, the object of the present invention is to provide a jettable color forming solution and a receiving media containing a color developer, thus forming an insitu chromophore for use in inkjet recording.
Another objective is to obtain water fastness without affecting stability to light.
Another objective is to obtain insitu chromophore formation below the surface of the receiving layer.
Another objective is to obtain chromophore having good stability to humidity and light.
Another objective is to obtain chromophore having excellent color gamut.
Another objective is to obtain an inkjet recording media having an extended color rendition.
It is a further objective to provide clear, light scatter-free recorded images for use on a transparent base. Another objective of the invention is to obtain images of superior luster and sharpness.
This invention proposes to achieve the above objectives by providing an inkjet recording system where the jetting head or cartridge contains solutions of color couplers of the photographic type. These heads or cartridges would contain a cyan dye coupler, a magenta dye coupler, and a yellow dye coupler. The receiver sheet would contain a color developing agent. Under the proper conditions of pH and oxidation (O), an insitu chromophore material would be formed. The general reaction would be the following. 
In all coupling reactions, an active methylene group and a p-phenylenediamine developer would be common. To the receiving layer or layers, a wide variety of additional elements may be added to further improve the pictorial, physical, and preserving properties of the images obtained when printing via a continuous or DOD inkjet printer.
This is also the option one has with the colorformer containing jettable solutions. A variety of items may be added to improve preserving qualities, density, image quality, water solubility, and reaction rate.
The jettable color coupler solution would be stored in a cartridge or reservoir of a DOD or continuous inkjet printer. The cartridge or reservoir would be an individual container for a cyan coupler, a magenta coupler, and a yellow coupler. Based on a digital data signal, the coupler solution would be jetted onto a receiver sheet containing a para-phenylenediamine color developer. The basic color reactions are the following, although not limited to these specific molecules. 
This is analogous to the color reaction in silver halide color photography. Thus one could envision all the benefits of that system""s dye hue, stability, and color gamut with the use of a white light digital system.
Since the color reaction would take place within the layer of the receiver, the image chromophore would be protected from smudging and handling marks. The chromophore formed would also be aggregated, waterproof and light-fade resistant. This would be a distinct advantage over present dye inkjet systems, fade in light and humidity conditions are common, while pigmented inkjet systems suffer from smudging and low opacity.
The receiving layer to which the jettable color coupling solution is jetted, be it DOD or continuous inkjet method, would have coated the color developing agents in the matrix. The receiver could be a single layer or multilayered. Inclusive in the layer or layers could be antioxidants, pH regulators, coupling accelerators, and the many options noted in the following pages. Oxidizing agent might also be part of the receiving matrix. In this case, the antioxidant and developing agent are preferably contained in a separate layer.
The color developing agents derived from p-phenylediamine meet the requirements of this invention. Preferred typical color developing agents used in the invention are 4-(N-ethyl-N-2-hydroxyethyl)-2-methylphenylenediamine sulfate (CD-4), 4-amino-n-ethyl-N(beta-methoxyethyl)-3-methylaniline-di-para-toluenesulfonic acid, and 4-(N-ethyl-N-2-hydroxyethyl)-2-methylphenylenediamine sulfate. Typical examples are listed below. 
Typical oxidizing agents meeting the requirements of the invention to initiate coupling reaction to form a dye are the following: oxygen, hydrogen peroxide, organic peroxides, potassium chlorate, ammonoum nitrate, and sodium iodate. Also preferred are systems where the oxidant is complexed with a macromolecule or polymer. Examples include polyvinyl pyrrolidone and cyclodextrin complexed with hydrogen peroxide.
Antioxidants of value in the practice of this invention could be compounds such as sodium sulfite, sodium bisulfite, phenidone B, phenidone-S, ascorbic acid and vitamin E.
The compounds that make up the imbedding matrix of the receiver sheet holding the various components of the invention include, in general, water soluble film forming polymers. However, this is not exclusive. In the right formulary, non-water soluble polymers could be used. These film forming water soluble polymers may include, for example, natural polymers or modified products thereof such as albumin, gelatin, casein, starch, gum Arabic, sodium alginate, hydroxyethyl cellulose, carboxylemethyl cellulose or xcex1- or xcex2-cyclodextrin and the like; polyvinyl alcohol; complete or partially saponified products of copolymers of vinyl acetate and other monomers; homopolymers or copolymers with other monomers of unsaturated carboxylic acids such as (meth) acrylic acid, maleic acid, crotonic acid and the like; homopolymers or copolymers with other vinyl monomers of sulfonated vinyl monomers such as vinylsulfonic acid, sulfonated styrene and the like; homopolymers or copolymers with other vinyl monomers of (meth)acrylamide; homopolymers or copolymers with other monomers of ethylene oxide; polyurethanes, polyamides having such groups as mentioned above; polyethyleneimine, polyacrylamides, water soluble nylon type polymers, polyvinylpyrrolidone, polyester; and so on. All these can also be used in mixtures.
These polymers can be blended with non-water soluble natural or synthetic high molecular compounds.
Suitable synthetic polymer materials can be chosen from among polyvinyllactams, acrylamide polymers, polyvinyl alcohol and its derivatives, polyvinylacetals, polymers of alkyl and sulfoalkyl acrylates and methacrylates, hydrolyzed polyvinyl acetates, polyamides, polyvinyl pyridines, acrylic acid polymers, maleic anhydride copolymers, polyalkylene oxides, methacrylamide copolymers, polyvinyl oxazolidinones, maleic acid copolymers, vinylamine.
Crosslinking agents suitable for this particular invention are selected depending on the water soluble polymer used.
They may include, for example, chromium salts (such as chrome alum or chromium acetate), aldehydes (such as formaldehyde, glyoxal or glutaraldehyde), N-methylol compounds (such as dimethylolurea or methyloldimethylhydantoin), dioxane derivatives (such as 2,3-dihydroxydioxane), activated vinyl compounds (such as 1,3,5-triacrylolyl hexahydro-s-triazine or bis(vinylsulfonyl)methyl ether), activated halogen compounds (such as 2,4-dicholo-6-hydroxy-s-triazine), amino or substituted-amino modified triazines, epoxies, carbamoylpyridinium compounds or mixtures of two or more of above mentioned crosslinking agents.
The layers and coatings can be modified by addition of fillers. Possible fillers of the kind are for instance clay, kaolin, talcum, Caxe2x80x94, Mg, or Ba-carbonate, Ca or Ba-sulphate, silica, titanium oxide, chalk, bentonite, zeolite, aluminum silicate, calcium silicate, silicium oxide, satin white, colloidal silicium oxide and the like. Likewise the possibility exists to use organic inert particles such as polymer beads. This includes beads that can be made from polyacrylates, polystyrene or different copolymers of acrylates and styrene. These fillers are selected according to the intended use of the printed image.
Some of these compounds cannot be used if the printed image is to be used as a transparency. Alternatively they are of interest in cases where the printed image is to be used as a reflected image. Often the introduction of such filler causes a desired matte surface.
The image recording elements of this invention comprise a support for the ink receiving layer. A wide variety of such supports are known and commonly employed in the art. They include, for example, those supports used in the manufacture of photographic clear films including cellulose esters such as cellulose triacetate, cellulose acetate propionate or cellulose acetate butyrate, polyesters such as poly(ethylene terephthalate), polyamides, polycarbonates, polyimides, polyolefins, poly(vinyl acetals), polyethers, polyvinyl chloride and polysulfonamides, Polyester film supports and especially poly(ethylene terephthalate) are preferred because of their excellent dimensional stability characteristics.
Likewise the usual supports commonly used in manufacturing of opaque photographic material can be used according to the present invention. They include baryta paper, polyethylene-coated paper, polypropylene synthetic paper, voided polyester as for instance manufactured by ICI under the trade name of MELINEX as well as voided polypropylene polyester likewise manufactured by the same company. Preferred are clear polyester, acetate, voided polyester or resin coated paper.
When such support material, in particular polyester, is used a subbing layer is advantageously added first to improve the bonding of the ink receiving layer to the support. Useful subbing compositions for this purpose are well known in the photographic art and include, for example, polymers of vinylidene chloride such as vinylidene chloride/acrylonitrile/acrylic acid terpolymers or vinylidene chloride/methyl acrylate/itaconic acid terpolymers. Also usable are plain paper, comprising a wide variety of sizing, cast-coated papers and aluminum foils.
The ink receiving layers or coatings according to this invention are in general coated from aqueous solutions or dispersions containing binders, additives, colorless pigments and the like. It is in many cases necessary to add surfactants to those coating solutions or dispersions allowing for smooth coating and evenness of the layers.
Examples of suitable surfactants are nonionic surface active agents such as saponin (steroids), alkylene oxide derivatives (such as polyethylene glycol, polyethylene glycol/polypropylene glycol condensates, polyethylene glycol alkyl or alkylaryl ethers, polyethylene glycol esters, polyethylene glycol sorbitan esters, polyalkylene glycol alkylamine or amides or silicone/polyethylene oxide adducts), glycidol derivatives (such as alkenylsuccinic acid polyglycerides or alkylphenol polyglycerides), aliphatic esters of polyhydric alcohol, alkyl esters of sucrose, urethanes or ethers; a sulfuric acid ester group or a phosphoric acid ester group, such as triterpenoid type saponin, alkylcarboxylates, alkylsulfonates, alkylbenzenesulfonates, alkylnaphthalenesulfonates, alkyl sulfuric acid esters, alkyl phosphoric acid esters, N-acyl-N-alkyltaurines, sulfosuccinates, sulfo-alkylpolyoxyethylene alkylphenyl ethers or polyoxyethylene alkyl-phosphates and cationic surface active agents such as alkylamine salts, aliphatic or aromatic quaternary ammonium salts (such as pyridinium or imidazolium salts) or phosphonium or sulfonium salt containing an aliphatic or heterocyclic ring. Equally suitable are fluorinated or perfluorinated derivatives of the above mentioned compounds.
Specific examples of these surface active agents are those described in e.g. U.S. Pat. Nos. 2,240,472, 1,831,766, 3,158,484, 3,210,191, 3,294,540 and 3,507,660; British Pat. Nos. 1,012,495, 1,022,878, 1,179,290 and 1,198,450; U.S. Pat. No. Nos. 2,739,891, 2,823,123, 3,068,101, 3,415,649, 3,666,478 and 3,756,828; British Pat. No. 1,397,218; U.S. Pat. No. 1,397,218; U.S. Pat. Nos. 3,133,816, 3,441,413, 3,475,174, 3,545,974, 3,726,683, and 3,843,368; Belgium Pat. No. 731,126; British Pat. Nos. 1,138,514, 1,159,825, and 1,374,780; 2nd U.S. Pat. Nos. 2,271,623, 2,288,226, 2,944,900, 3,253,919, 3,671,247, 3,772,021, 3,589,906, and 3,754,924 all incorporated by reference.
Besides being necessary for coating purpose, surfactants may have an influence on the quality of the generated images and may therefore be selected with this specific goal in mind. There is in general no limitation to the use of the types of surfactants used.
Typically the receiving layers according to this invention have a thickness in the range of 0.5 to 30 microns, preferably in the range of 2.0 to 15 microns dry thickness. The coating solutions or coating dispersions can be coated onto a support by any number of suitable procedures. Usual coating methods include immersion or dip coating, roll coating, air knife coating, extrusion, doctor blade coating, rod and/or blade metering, or by spraying. An ink receiving system can be built up by several layers.
These layers can be coated one after the other or simultaneously. It is likewise possible to coat a support on both sides with ink receiving layers.
Alternatively, the backside may be coated with auxiliary layers like for instance anticurl layers or antistatic layers. The way however by which the claimed receptive layers are produced is not to be considered limiting for the present invention.
In addition to the above mentioned elements, ink receiving layers, as claimed in this invention, can contain additional additives aimed at improving appearance as well as performance of the produced imaging material. It can, for instance, be beneficial to add brightening agents to the layers of receiving sheets. There is in general no limitation as to the kind of brighteners used. Suitable brightening agents are for instance stilbenes, coumarines, triazines or oxazoles or others known in the art.
Light stability can in general be improved further by adding UV absorbers to the layers. Although UV absorbers are in general added to the topmost layer of the system there is no limitation as to where within the ink receiving element such light absorbing compounds are added. The amount of UV-absorber can vary from 200-2,000 mg/m2 , preferably however from 400 mg to 1,000 mg/m2. Suitable types of absorbers can be for example benztriazoles, benzophenones, derivatives of acrylonitrile, thiazolidone, oxazole and thiazole.
It is further known that images can be protected from degradation by the addition of light stabilizers and antioxidants. Examples of such compounds are among others sterically hindered phenols, sterically hindered amines, chromanols and the typical antioxidants include nitrate salts, gallate esters, tocopherol, mercapto heterocycles, and sulfite salts.
Above mentioned additives can, if water soluble, be added as aqueous solutions. In the case where these compounds are not water soluble, the above mentioned additives can be incorporated in the ink receiving element by common techniques known in the art. The compound is typically dissolved in a solvent selected from organic solvents compatible with water, such as alcohol, glycol, ketones, esters, amides and the like. Alternatively the compounds can be added to the layer as fine dispersions, as oil emulsions, as a cyclodextrin inclusion complex or loaded as fine dispersions onto latex particles. Ultrasound or milling can be used to dissolve or disperse marginally soluble additives.
Inks for ink jet printing are well known. These inks consist in essence of a liquid vehicle and dissolved or suspended therein a dye or pigment. The jettable solution in this invention would not be a dye or pigment, but a colorless solution of a color coupler having the ability to form a dye or pigment when contacting the receiver sheet containing the color developing agent.
The liquid vehicle of the color couplers employed in this invention consist in general of water, a compound for control of pH (NaOH, KOH, etc.), and an oxidizing agent. Usable oxidizers include hydrogen peroxide, oxygen, mercuric chloride, potassium chlorate, ammonium nitrate, ammonium picrate, and organic peroxides.
The invention should not be limited to these specific compounds but could include other oxidizing agents that do not impart color to the matrix and have the capability of oxidizing the paraphenylene developing agent. The general class of compounds to be used as color coupling agents that form cyan, magenta, and yellow chromophoric materials would have an active methylene group contained in the molecule. Specific examples of these color coupling types are contained herein below. The invention is not limited to these specific examples. Any compound having an active methylene group capable of forming a chromophore with a color developer would be included. Also a combination of these couplers could be used. 
Other compounds that might be contained in the jettable color coupling solution could be water miscible organic components such as ethylene glycol, higher molecular glycol, glycerin, dipropylene glycol, polyethylene glycol, amides, polyvinypyrrolidone, N-methylpyrrolidone, cyclohexylpyrrolidone, carboxylic acids, and esters, ethers, alcohol, organsulfoxides, sulfolane, dimethylforamide, triethylamine, dimethylsulfoxide, cellosolve, polyurethanes acrylates and the like.
Aqueous compatible components of the printing solution generally serve as humecfactant, cosolvent, viscosity regulating agent, penetrating agent, leveling agent or drying agent. These components, typically organic, have in most cases a boiling point higher than that of water. In addition, aqueous inks may contain inorganic or organic salts to impart electrical conductivity. Examples of such salts include nitrates, chlorides, phosphates and the like. Organic acid of low molecular such as acetic, oxalic and similar may also be used.
Other additives present in the jettable coupler solution might be surfactants, optical brighteners, UV absorbers or light stabilizers, biocides and polymer additives. This description of jettable color coupler solutions is for illustration only and not to be considered as limiting the invention.